Putrescine (or 1,4-butanediamine) is an important raw material for the production of polyamide-4,6 including nylon-4,6, and is mainly produced on an industrial scale by the hydrogenation of succinonitrile, which is produced from acrylonitrile by addition of hydrogen cyanide. The chemical synthesis of this compound requires non-renewable petrochemical products as raw materials, and relatively high temperature and pressure in a multi-step and multi-reactor design, as well as the use of expensive catalyst systems. Furthermore, since these raw materials are highly toxic and flammable, the known chemical synthetic processes are environmentally disadvantageous. Accordingly, as an alternative to the chemical production process, a process of producing putrescine from a renewable biomass-derived carbon source is required. Recently, a biochemical process of producing putrescine by environmentally friendly microorganisms has received much attention. Putrescine is a kind of polyamine which is found in a broad spectrum of organisms ranging from bacteria to animals and plants. The concentration of putrescine in E. coli is known to be extremely high, as much as about 2.8 g/L. Also, microorganisms have potentially good resistance to high concentrations of polyamines, and thus they are able to grow and survive in the presence of high concentrations thereof. For example, it has been reported that Corynebacterium glutamicum can grow even in the presence of more than 30 g/L of cadaverine. Accordingly, Studies have been continuously conducted to use microorganisms in the production of industrially available high-concentration polyamines. However, studies on the production of polyamines using microorganisms have not advanced enough to be industrially applicable. Therefore, it is aneed to develop a strain capable of producing polyamines in a high yield (Qian Z G, et al., Biotechnol Bioeng, 104: 651-662, 2009; Schneider J, et al., Appl Microbiol Biotechnol, 88: 859-868, 2010).
Meanwhile, ornithine decarboxylase (ODC) is an enzyme found in most microorganisms which converts ornithine into putrescine. ODC in E. coli generally forms a homodimer, and active sites are formed at the dimer interface. The reaction mechanism of ODC requires pyridoxal phosphate (PLP) as a cofactor, and PLP forms a Schiff base at a lysine residue of the active site of the enzyme, which is later displaced by a substrate ornithine that undergoes decarboxylation. When putrescine is produced, ODC again forms a Schiff base with PLP.
When ODC introduced into a putrescine-producing strain, genus Corynebacterium, is a protein encoded by E. coli speC gene, and its activity is reported to be very low. Therefore, in order to develop a strain producing putrescine in a high yield, improvement of ODC, which is an enzyme involved in the final step of the putrescine biosynthetic pathway, is very important. Until now, mutation researches have been performed only to the structure or reaction mechanism of an ODC protein, and there have been no reports regarding an increase activity thereof.